The LDR (component R213) is not mounted on AVR Butterflies produced after 2006-07-01. This because there is no replacement that meets the RoHS standard. On these kits there is added a resistor to avoid a floating input to the ADC. This resistor is placed on the backside of the PCB, and marked with a red line around it in the picture below.
There are four holes where the LDR should be mounted, but only two are needed. This is just to have a dual footprint with different pitch between the holes. The LDR pins should be mounted in either horizontal or vertical direction, in the holes most suitable. The original LDR was mounted vertically. See the BOM and Schematics page for more information on the LDR.
ยท The Voltage regulator diode (component D200) is not mounted on AVR Butterflies produced after August 2005. Due to end of life of component.